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Swallowtail (Papilio machaon)

On this page, we have made available all the information we have for this species

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Picture of Swallowtail
© Nick Greatorex-Davies

The Swallowtail has a highly restricted distribution in Britain occurring only in the open fens and marshes of east Norfolk where its foodplant Milk-parsley (Peucedanum palustre) grows. It was formerly more widespread. (For further details on this species see

Family : Papilionidae

Status : Stable

Status details :
Status since 1976 is Stable with a increase of 57%
Status over the last 20 years is Stable with a decrease of -25.2%
Status over the last 10 years is Stable with a decrease of -51.6%

Log collated index plot

Species Log Collated Index Plot

This chart shows the index of abundance (LCI = Log Collated Index) over time. It shows fluctuations in populations from year to year, and is scaled so that the average index over the whole series is equal to 2 (horizontal line). For greater detail about how this index is derived, click on the green question mark above.

Trend description :
Counts at Bure Marshes in Norfolk, the only UKBMS transect where this species has been regularly recorded for long enough to calculate a trend in abundance, indicate that the population of this species at the site is increasing. Recently more sites have been added to the database and appear to confirm this trend with a significant long-term increase across all sites since monitoring began.

This map shows the distribution between 1995 and 2016. Data is derived from the Butterflies for the New Millenium dataset via the NBN Gateway

Phenology plot
Species Phenology Plot

Phenology plot

This chart shows the average number of butterflies seen on transects between Arpil and October across all sites (fitted values from a Generalised Additive Model). The blue line gives average counts over the full BMS series (1976 to date) and the red line gives the average for the last year.

Species abundance map


This map shows symbols for the mean abundance at transect sites, with the colour of the symbol reflecting the level of abundance. Means are over all years. Grey background squares are the occupied cells as shown by the Butterflies for the New Millenium over the previous ten year period.


In total, Swallowtail has been recorded from 114 transects in the Butterfly Monitoring Scheme. Of these, annual indices of abundance have been calculated from 4 sites, with an average index of 0 individuals per site.

For 0 of these sites, Swallowtail has been recorded well enough to calculate annual indices of abundance in more years, allowing trends to be calculated.

In 2019, 35 individuals were recorded from 3 sites, producing annual indices at 0 of these.

The UK Butterfly Monitoring Scheme is organized and funded by Butterfly Conservation (BC), the UK Centre for Ecology and Hydrology (CEH), the British Trust for Ornithology (BTO), and the Joint Nature Conservation Committee (JNCC). The UKBMS is indebted to all volunteers who contribute data to the scheme.